Is it question from some test? **X-Ray** - It's basically a diffraction at quantum level. > While diffraction occurs whenever > propagating waves encounter such > changes, its effects are generally > most pronounced for **waves whose > wavelength is roughly comparable to > the dimensions of the diffracting > object** or slit. [Diffraction - Wikipedia][1] **NMR** - Found on **absorption/emission** effect. Here you don't need comparable sizes of wavelenght and object. What's matter here is a difference in two energy states (difference in energy levels of spin states, for 1H -1/2 ; 1/2) that must be exact as an energy of radiofrequency waves. It's comparable with **UV/VIS** spectroscopy. Absorption of light waves energy to excite electrons, and emission when they relax to ground state. [1]: http://https://en.wikipedia.org/wiki/Diffraction